Yeast contains nutritive components and abundant taste components such as nucleic acids, amino acids, and peptides. Yeast extract, which is an extract thereof, is used in a broad range of fields, such as in natural seasonings and health foods, and as a culture for microscopic organisms. Various methods of producing yeast extract are known which use extracting enzymes, mediums, and the like. Examples include the method of Patent Literature 1.
Yeast cell bodies in which yeast extract has been extracted from yeast have, as principal components, a cell wall component of glucan, mannan, and the like; and proteins; lipids; and the like. There are several known publications regarding processing and methods of effectively using these yeast cell bodies. For example, Patent Literature 2 teaches a method of treating a yeast extract extraction residue solubilized using a specific enzyme in waste water treatment. Patent Literature 3 describes a method of producing mannose by causing yeast cell bodies of a yeast extract extraction residue to be assimilated by microorganisms. Patent Literature 4 describes a method of obtaining a medicinal compound by alkali treatment of a yeast cell body residue from which yeast extract has been extracted, followed by irrigation thereof. Patent Literature 5 describes a method of obtaining a microorganism culture substrate material by allowing a cell wall lytic enzyme or the like to act on yeast cell bodies from which yeast extract has been extracted.
However, due to products having a low added value relative to processing costs, or due to a low amount of consumption of yeast extract extraction residue in each application, none of these methods have been put into practice or managed to dramatically reduce an amount of yeast extract residue.
There are also reports, as in Patent Literature 6, focusing on dietary fiber contained in the yeast cell wall fraction from which yeast extract has been extracted. Dietary fiber or a composition including a large amount thereof is presently in use in a variety of applications such as as a functional ingredient in health food or foodstuff, as a physicality enhancer, and the like. Glucan and mannan contained in the yeast cell wall are refined using various methods and are widely utilized as a health food, a functional ingredient, animal feed, and the like. In particular, β-1,3-1,6-glucan has many functions that are being widely studied throughout the world, such as an antitumor effect, an immunostimulator effect, and the like. In recent years, extremely low molecular weight β-1,3-1,6-glucan has been reported to have an antioxidant effect as well. In addition, mannose, which is refined from mannan, has also received attention as a functional food. However, when used as-is, a yeast cell wall composition (as a yeast extract extraction residue) has many impurities and a low dietary fiber content. Therefore, Cited Reference 6 describes the necessity of chemical treatments such as alkali ethanol treatment, alkali/acid treatment, and the like; and physical treatments such as homogenization as methods to remove impurities. Chemical methods such as alkali ethanol treatment and alkali/acid treatment are unlikely to be put into actual use due to questions of food safety and because a great quantity of drugs are produced as waste products. Meanwhile, homogenization treatment uses costly machinery and equipment, and is also unlikely to be put into actual use. Besides these chemical and physical methods, methods utilizing enzymes have also been investigated. However, yeast cell walls are primarily composed of the dietary fibers glucan and mannan as well as protein and lipids, which form strong and complex conjugates. Therefore, the yeast extract residue is not particularly susceptible to the action of a typical enzyme, and even when susceptible the yeast extract residue is unlikely to break down, making it difficult to increase dietary fiber content any further without chemical methods or mechanical pulverization.
Given the above, there is currently little value in using great quantities of yeast cell bodies from which yeast extract has been extracted, which is produced as part of the production of yeast extract. A remainder utilized as fertilizer and animal feed and the like is currently treated as industrial waste.
Additionally, Patent Literature 7 describes being able to obtain a savory seasoning by hydrochloric acid hydrolysis or enzymatic degradation of protein from, for example, livestock meat, fish meat, soy beans, wheat, or corn.